In the technique, evermore complicated strand profiles made of rubber, in particular sponge rubber, are needed. These serve, for example, as sealing strips for doors and windows in buildings, in the automobile industry, in refrigerator construction and in many other branches of industry. These profiles have not only a complicated outer form but often have inner hollows and chambers so that in use these profile strips can be compressed to a very small volume whereby the profile itself may often assume an angle form or wave form cross section and must be so formed that it remains elastic even after long use must not tear or crack or be torn from the usual angle form support on which it is mounted. These requirements of rubber profiles, in particular sponge rubber profiles, make it necessary that the profile strand must be uniformly vulcanized throughout its cross section and over its whole length and must have no portions in which overheating or possibly even burning may have been caused by too strong local energy concentration.
Such complicated rubber profiles, in particularly of sponge rubber, can be vulcanized only in a substantially uniform UHF-energy field. UHF-energy is electro-magnetic energy which lies in the range of milimeter waves, centimeter waves and decimeter waves. Such energy is for the most part produced in magnetrons and is conducted through wave guides in the form of tubular conductors of round or rectangular cross section to a resonator chamber in which this energy acts on the product to be heated and thereby vulcanized. The diffiiculty of heating with UHF-energy is the problem of obtaining a suitable uniform field distribution in the resonator chamber. Non-uniform distribution leads to local overheating or indeed burning or, on the other hand, to insufficient heating and thereby unvulcanized portions. Uniform field distribution is very difficult to obtain. When a uniform field distribution in an empty resonator chamber has been achieved with the help of a measuring probe, this distribution is disturbed by the product to be heated so that it becomes non-uniform.
This difficulty is also experienced in microwave ovens for heating food. In order to reduce it, it has been proposed to divide the wave guide and direct the energy into the resonator chamber by two split beams which are disposed at an angle of 90.degree. to one another. This leads to a certain improvement in uniformity of the field because there are two fields at right angles to one another in the resonator chamber. This may be sufficient in the case of heating food. As food always contains water, no burning can occur until the water is fully evaporated. This requires very substantial local concentration of energy since considerable heat is required to convert water in the fluid state to a gaseous state. It is otherwise with the heating of water-free products such as rubber products. Here the danger of the occurrence of burning at places of high energy concentration is much greater because here there is no heat of vaporization available.